Abstract
In the first report about the salivary oxidation catalyst detectable with rifam- picin as a substrate, the author introduced from several points of view that the catalyst should be a low molecule peptide enzyme with copper at its active center, namely, a relatively unstable substance, detectable in a salivary fraction consisting of peptide which can be eluted by Sephadex gel-filtration, pH dependent activation, and complete inhibition by H2S, cysteine, cyanides, citrate, methanol and ethanol. The oxidation catalyst was further named tentatively naphthohydroquinone de- hydrogenase.
The present paper reports on investigations on the oxidation mechanism of rifampicin by the salivary catalyst, and a significant individual difference in the oxidation activity of saliva.
On gasometric analysis of molecular oxygen uptake in the reaction system, it was found that the oxidation activity of the catalyst fraction, which had been isolated from saliva by Sephadex G-25 gel-filtration, correlated well to the molecular oxygen uptake accompanied by catalytic oxidation of rifampicin. This finding may be an evidence to show that hydrogen liberated by oxidation of rifampicin is accepted by molecular oxygen.
Upon investigation of catalytic oxidation of rifampicin with heavy metals, it was observed that the oxidation was developed only in the presence of divalent copper out of several investigated metals: iron, copper, zinc, cobalt, lead, silver and mercury. But with divalent copper, for example CuCl2, the catalytic oxidation was not so significant at pH below 3, necessary to activate completely salivary catalyst. In the meanwhile, an apparent oxidation was observed rather at pH over 4, unable to activate a salivary catalyst. However, the catalytic oxidation by divalent copper may suggest probably that the heavy metal contained in the salivary catalyst is copper
Rifampicin could also be oxidized promptly and completely in the presence of ferricyanide under an acid condition. However, this phenomenon seemed to be that the rifampicin oxidation was not developed catalytically, but resulted from an oxidative action of ferricyanide well known as an oxidant, and it was supported by this fact that any other ferric compound not only catalysed no oxidation of rifampicin but also was an inhibitor of a salivary catalyst.
In comparing one with another catalytic oxidation of rifampicin with various, salivas, namely those which had been sampled from different subjects under the same condition, it was noted that there was a significant individual difference in the oxida- tion activity of saliva. It was further confirmed that the oxidation activity of indi- vidual saliva was considerably reproducible in duplication tests, and that the activity order was not so varied, even though analysis was carried out in the corrected activities of which the oxidation activity was divided by the 280 mp extinction of the fraction itself, respectively.
